Script to append a new axis to fvar and related variation tables

add_fvar_axis.py

import sys
import argparse
import logging

from fontTools.ttLib import TTFont
from fontTools.ttLib.tables._f_v_a_r import Axis
from fontTools.varLib.builder import buildVarRegionAxis


log = logging.getLogger("add_fvar_axis.py")


def main():
    parser = argparse.ArgumentParser(description="Add a new axis to a variable font.")
    parser.add_argument("font", help="The font to modify")
    parser.add_argument("axis", help="The axis tag=min,default,max", nargs="+")
    parser.add_argument("-o", "--output", help="The output font")
    parser.add_argument("-v", "--verbose", action="store_true")

    args = parser.parse_args()

    logging.basicConfig(level="DEBUG" if args.verbose else "INFO")

    font = TTFont(args.font, lazy=False)
    font.ensureDecompiled()

    fvar = font["fvar"]
    name = font["name"]
    for axis in args.axis:
        tag, values = axis.split("=")
        values = [float(v) for v in values.split(",")]
        axis = Axis()
        axis.axisTag = tag
        axis.minValue, axis.defaultValue, axis.maxValue = values
        axis.axisNameID = name.addName(tag, platforms=((3, 1, 0x409),))
        fvar.axes.append(axis)
        for instance in fvar.instances:
            instance.coordinates[tag] = axis.defaultValue

    avar = font.get("avar")
    if avar is not None:
        segments = avar.segments
        for axis in fvar.axes:
            if axis.axisTag not in segments:
                segments[tag] = {-1.0: -1.0, 0.0: 0.0, 1.0: 1.0}

    for tableTag in font.keys():
        table = font[tableTag]
        if (
            getattr(table, "table", None) is None
            or getattr(table.table, "VarStore", None) is None
        ):
            continue
        log.info(f"Updating {tableTag}.VarStore")
        varStore = table.table.VarStore
        for region in varStore.VarRegionList.Region:
            for _ in range(len(args.axis)):
                region.VarRegionAxis.append(buildVarRegionAxis((0, 0, 0)))

    if args.output:
        font.save(args.output)


if __name__ == "__main__":
    main()